Fertilization
~ Can occur up to 24 hours after ovulation
~ Occurs in the widest part of the tube (ampulla)
~ When sperm binds it releases an acrosomal enzyme
~ Sperm forms an acrosomal apparatus
~ Cortical Reaction
Acrosomal Enzyme
~ Allows head of sperm to penetrate the corona radiata and zona pellucida
Acrosomal Apparatus
~ Extends and penetrates the cell membrane
~ Pronucleus may freely enter oocyte once meiosis 2 has finished
Cortical Reaction
~ Release of Ca2+ ions
~ Depolarize the membrane of the ovum (prevents further fertilization
~ Increases the metabolic rate of the newly formed diploid zygote
Fertilization Membrane
~ Impenetrable and depolarized membrane
Twins
~ Dizygotic or fraternal
~ Monozygotic or identical
Dizygotic or fraternal
~ Fertilization of 2 different eggs released during one ovulatory cycle by two different sperm
~ Each zygote implants and develops its own placenta, chorion and amnion
~ Sometimes the placentas will fuse
Monozygotic or identical
~ Single zygote splits into 2
~ If incomplete division = conjoined twins
~ How much they share in utero depends on how early separation occurs
Monochorionic/monoamniotic
~ Twins share the same amnion and chorion
Monochorionic/diamniotic
~ Each have their own amnion, but share the same chorion
Dichorionic/diamniotic
~ Each have their own amnions and chorions
Cleavage
~ Zygote undergoes rapid mitotic cell divisions
First Cleavage
~ Creates the embryo
~ Several rounds of mitosis
~ Size remains unchanged (increase in nuclear to cytoplasmic ratio and SA to V ratio) aka more area for gas and nutrient exchange
Characteristic of Zygote
~ Unicellular
2 Types of Cleavage
~ Indeterminate
~ Determinate
Indeterminate
~ Cells that can still develop into complete organisms (monozygotic twins)
Determinate
~ Cells fate is already determined
~ Committed to differentiating into a certain type of cell
Embryo becomes a....
~ Morula
Morula
~ Solid mass of cells
~ From term mulberry
Morula undergoes...
~ Blastulation at 16-cell stage
Blastula
~ Hollow ball of cells with fluid-filled inner cavity known as blastocoel
Blastocyst
~ Mammalian blastula
~ Contains trophoblast cells and inner cell mass
Trophoblast
~ Surround the blastocoel and give rise to chorion and then the placenta
Inner Cell Mass
~ Protrude into the blastocoel and gives rise to organism
Blastula moves through...
~ Fallopian tube into the uterus
~ Burrows into the endometrium
Trophoblast cells are specialized to create...
~ Interface between maternal blood supply and developing embryo
Chorion
~ Extraembryonic membrane that develops into the placenta
Chorionic Villi
~ Microscopic finger-like projections that penetrate endometrium
~ Develop into the placenta and support maternal-fetal gas exchange
Embryo connected to the placenta via the
~ Umbilical Cord
Umbilical Cord
~ 2 arteries and 1 vein encased in gelatinous substance
~ Vein carries freshly oxygenated blood with nutrients to baby and arteries carry waste and deO2
Until Placenta is functional...
~ Embryo is supported by yolk sac
Yolk Sac
~ Site of early blood cell development
Allantois
~ Involved in early fluid exchange between the embryo and yolk sac
~ Umbilical cord is formed from this
Amnion
~ Surrounds allantois
~ Thin, tough membrane filled with amniotic fluid (shock absorber)
Gastrulation
~ Generation of three-distinct cell layers
Gastrula
~ Formation of an invagination and the elimination of blastocoel
Archenteron
~ Membrane invagination into blastocoel
~ Develops into the gut
Blastopore
~ Opening of the archenteron
Blastopore develops into...
~ Anus in deuterostomes
Primary Germ Layer
~ Ectoderm
~ Mesoderm
~ Endoderm
Ectoderm
~ Rise to the integument (epidermis, hair, nails, lens, nervous system, inner ear)
Mesoderm
~ Develops into several systems (musculoskeletal, circulatory and most of the excretory system)
~ Rise to gonads as well as muscular and connective tissue
Endoderm
~ Forms the epithelial linings of the digestive and respiratory tracts (pancreas, thyroid, bladder and distal urinary tracts as well as parts of the liver)
Differentiation
~ Cell develops into distinctly different cell types
~ Changes in structure, function and biochemistry
Selective Transcription
~ Genes needed for a particular cell type are transcribed
Induction
~ Ability of one group of cells to influence the fate of other near by cells
Inducers
~ Growth factors
~ Mediate induction
~ Diffuse from organizing cells to responsive cells
~ Responsible for guidance of neuronal axons and proximity of different cell types
Neurulation
~ Development of the nervous system
Neurulation: 1
~ Rod of mesodermal cells (notochord) forms long axis and induces a group of ectodermal cells t slide inward and form a neural fold which surround a neural groove
Neurulation: 2
~ Neural folds grow towards one another until they fuse into the neural tube and gives rise to the central nervous system at tip of fold are neural crest cells
Neural crest cells
~ Migrate outward to form the peripheral nervous system and some other tissues
Neurulation: 3
~ Ectodermal cells will migrate over the neural tube and crests to cover the rudimentary nervous system
Teratogens
~ Substances that interfere with development, causing defects or even death of developing embryo
~ Genetics of individual embryos effect the teratogen
What affects outcome of teratogen?
~ Route of exposure, length of exposure, rate of placental transmission of the teratogen, and the exact identity of the teratogen
Common Teratogens
~ Alcohol
~ Prescription Drugs
~ Viruses
~ Bacteria
~ Environmental Chemicals
Maternal Health
~ Certain conditions may cause changes in the overall physiology of the mother, resulting in overexposure or underexposure of the embryo or fetus to certain chemicals
~ Overexposure to sugar = hypoglycemia
~ Folic Acid = Spina bifida or anencephaly
Determination
~ Commitment to having a specific function
~ Before: can be any cell
~ After: Commited
~ Occurs if asymmetrical distribution of mRNA between 2 daughter cells, secretion of specific molecules from nearby cells = morphogens
Morphogens
~ ause nearby cells to follow a particular developmental pathway
Stem Cells
~ Cells that have not differentiated or give rise to other cells that differentiate
Potency
~ Determines the tissues that stem cells can differentiate into
Totipotent
~ Greatest potency and can differentiate into any cell type (embryonic stem cells)
Pluripotent
~ Differentiate into any cell but placental
Multipotent
~ Differentiate into multiple types of of cells within a group
Responder
~ Cell that is induced
Competent
~ Able to respond to a signal and become a responder
Autocrine
~ Same cell
Paracrine
~ Local area
Juxtacrine
~ Cell directly stimulation receptors of adjacent cell
Endocrine
~ Hormones in bloodstream
Growth Factors (Inducers)
~ Peptides that promote differentiation and mitosis in certain cell tissues
~ Expressed depending on location
Reciprocal Development
~ When the tissue signals the growth factor to trigger growth in the tissue;
Morphogens can
~ Diffuse
Common Morphogens
~ Transforming growth factor beta (TGF_B)
~ Sonic Hedgehog (Shh)
~ Epidermal Growth Factor (EGF)
Cell Migration
~ Cells must be able to disconnect from adjacent structures and migrate to their anatomically correct location
~ NC cells undergo extensive migration
Cell Death
~ Apoptosis
~ May occur via apoptotic signals or preprogramming (separation of fingers)
~ Cell undergoes morphological changes
Apoptotic Blebs
~ Self-contained pieces
~ Recycling of materials
~ Contained in a membrane
Necrosis
~ Cell death as a result of injury
Regenerative Capacity
~ Ability of an organism to regrow certain parts of the body
~ Stem cells migrate to the necessary part of the body to initiate growth
Complete Regeneration
~ Lost or damaged tissues are replaced with identical tissues
Incomplete Regeneration
~ Newly formed tissue is not identical in structure or function to the tissue that has been injured or lost
~ Typically found in humans
Regenerative capacity varies by tissue type
~ Liver = high
~ Heart = little to none
~ Kidney = moderate
Senescence
~ Biological aging, occurs as these changes accumulate and can occur at the cellular and organismal level
Senescence in Cells
~ Failure to divide after 50 divisions in vitro
~ May be due to shortened telomeres which prevent the loss of genetic information and prevent unwinding
Telomere
~ High [ ] of guanine and cytosine knot
Telomerase
~ Allows cells to divide indefinitely
~ Synthesizes end of chromosomes and prevent senescence
Senescence in Organisms
~ Changes in the body's ability to respond to changing environment
Fetal blood cells contain...
~ Fetal hemoglobin
~ Greater affinity for oxygen
~ Assists in the transfer and retention of oxygen
Placental Barrier Function
~ Immune protection
~ Fetus = immunologically naive
~ Crossing of antibodies across placental barrier = protection
~ Endocrin Organ (Produces progesterone, estrogen, and human chorionic gonadotropin)
Pathogens that can cross barrier
~ TORCHES stands for TOxoplasma gondii, Rubella, Cytomegalovirus, HErpes or HIV, and Syphilis.
Circulatory System in Fetus
~ Lungs and liver do not serve significant function
~ Gas exchange at the placenta
~ Detox and Metab in mother's liver
~ Organs sensitive to high pressure, so three shunts to drive the blood away
Fetal Heart
~ From lungs: foramen ovale, one-way valve connects the right and left atrium
~ Right side is at higher pressure, when the pressure reverses at birth the shunt closes
~ Ductus Arteriosus: blood from pulm. artery to aorta
~ Ductus Venosus: blood from place
Gestation
~ 266 days
~ 3 trimesters
First Trimester
~ Major organs develop
~ Heart beats at 22 days
~ Eyes, gonads, limbs, and liver start to form
~ 5 weeks - 10 mm, 6 weeks - 15mm
~ 7 - cartilaginous skeleton begins to harden into bone
~ 8 - most organs developed and brain is fairly developed = fetus
~ 3
Second Trimester
~ Fetus undergoes tremendous amount of growth
~ Moves within amniotic fluid
~ Face = more human and fingers elongate
~ End of 6 months fetus = 30-36 cm
Third Trimester
~ Continues rapid growth and brain development
~ 9: Antibodies transport from M to F for protection against foreign matter
~ Growth rate slows and fetus becomes less active, b/c less room
Birth
~ Rhythmic contractions of uterine smooth muscle coordinated by the prostaglandins and oxytocin
~ Cervix thins out and amniotic sac ruptures
~ Strong uterine contractions result in birth of fetus
~ Placenta and umbilical cord are expelled (after birth)